<?php

$pdo = new PDO("firebird:dbname=localhost:/var/lib/firebird/data/marco.gdb;charset=utf-8", "sysdba", "m1d0ry!!");
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->setAttribute(PDO::ATTR_AUTOCOMMIT, false); 

$sql = "insert into test(nombre) values ('marco') returning id";

$pdo->beginTransaction(); 
$qry = $pdo->prepare( $sql );
$qry->execute();

$returned_id = $qry->fetchColumn(); 

$pdo->commit(); 

$pdo->setAttribute(PDO::ATTR_AUTOCOMMIT, true);

print_r($returned_id);